1. Field of the Invention
The invention disclosed and claimed herein generally pertains to a compact thermal sensor apparatus for monitoring temperature in an integrated circuit (IC) or other semiconductor package. More particularly, the invention pertains to sensor apparatus of the above type that comprises two or more components, wherein each component is located on a different layer of the IC. Even more particularly, the invention pertains to a sensor apparatus of the above type wherein wiring channels for IC functions unrelated to the thermal sensor can readily be routed through any of the sensor components.
2. Description of the Related Art
It is generally important to monitor the internal temperature of an integrated circuit such as a microprocessor or the like. Typically, an analog thermal sensor for integrated circuits comprises a metal line or wire of substantial length and a fixed width. From the designed length of the sensor wire and the resistivity of the material used therefor, the over-all resistance of the sensor wire can easily be measured, by passing a known current through the wire and measuring the voltage thereof. Moreover, a material is selected for the sensor wire that has a resistance which will change as a linear function of temperature, over a specified temperature range. From the linear relationship between resistance and temperature, it is comparatively easy to determine temperature proximate to the sensor from the measured sensor resistance, and also to predict other corresponding values of resistance to temperature. The accuracy and sensitivity of the temperature measurement is determined primarily by the physical properties of the metal used for the sensor wire, and by the cross-section and length of the wire sensor. Variations in the cross-section of the sensor wire are dictated by variations in the wire fabricating process.
In the past, a wire thermal sensor of the above type has generally been constructed by placing the entire wire on a single metal layer or level of an IC, in a serpentine pattern or configuration. ESD diodes are placed at either end of the sensor wire, to protect the IC semiconductor from high voltage transients. Such prior art arrangement is shown in FIG. 1, as described hereinafter. However, this arrangement has a number of drawbacks. The long length of the serpentine line, when constructed on only a single layer of the IC, causes a large amount of the layer area to be used for the sensor circuit. Thus, the sensor configuration can significantly reduce the wiring channels on that layer and hence, the sensor cannot be an integral part of a circuit being measured.
Moreover, it would often be useful to be able to position a temperature sensor at any desired location in an IC. For example, there could be concern of a hot spot developing at a particular IC location, due to substantial power dissipation. However, because of the limitations of currently available sensors, it could be difficult to place one of such sensors at the particular location, in order to monitor location temperature.
In a prior art thermal sensor of the above type, there are conflicting requirements in that the sensor wire needs to be narrow enough to provide enough resistance over-all, but must still be wide enough that the sensor itself does not generate heat. Also, the use of narrow width lines or wires makes the sensor more susceptible to variations in the wire fabrication process, since process variations tend to vary by some percentage around a mean value. Presently, there is an optimum range of resistance for a sensor of this type. If the value is too high, the value cannot be measured by available measurement tools. If the resistance is too low, it becomes too insensitive. Process variations limit how close the design can be made to the high side of the optimum resistance range.
It would be desirable to provide a thermal sensor for integrated circuits that could overcome the above problems and disadvantages found in the prior art.